1. Field of the Invention
The present invention relates generally to a method and an apparatus for grinding ferrules for ribbon type optical fibers used for a ribbon type optical fiber connector, an optical attenuator and other optical circuit component each of which is used for the purpose of accomplishing a multi-core type integral connection in an optical fiber communication circuit system. More particularly, the present invention relates to a method and an apparatus for grinding the foremost end surfaces of ferrules for ribbon type optical fibers in consideration of the contour of each ground surface after completion of a grinding operation wherein an undesirable loss due to reflective return of an incident light beam at a joint end surface of each optical circuit component can be minimized.
2. Description of the Related Art
At present, many optical components such as optical connectors each used for connecting an opposing pair of ferrules to each other, optical attenutaors each used for attenuating the intensity of an incident light beam, optical branching/coupling units each used for branching an optical signal or coupling optical signals to each other have been employed in optical fiber communication circuit systems.
As the number of application fields for optical fiber communication circuit systems increases year by year, not only the number of optical circuit components but also the time and cost required for laying optical fibers throughout a communication circuit system are increased and enlarged enormously.
To solve the foregoing problem, a proposal has been made as to a method of providing so-called ribbon type optical fibers each composed of four to twelve optical fibers arranged in a flat plate-shaped configuration. In practice, ribbon type optical fibers have been put into practical use for communication circuit systems and their fields of application have rapidly expanded year by year.
When an optical fiber communication circuit system is built by using a number of optical fibers, the number of joint locations where optical fibers are jointed to each other increases unavoidably. Especially, in a case where a high speed optical fiber communication system having a large capacity is built in the same manner as mentioned above, there is a need to take account of a substantial loss due to reflective return of an incident light beam at a joint location as well as a joint loss due to connection of optical fibers to each other in the communication circuit system.
To facilitate understanding of the present invention, a conventional optical connector employable for ribbon type optical fibers will briefly be described below with reference to FIGS. 8(a) and 8(b).
FIG. 8(a) is a sectional plan view of a conventional typical optical connector for a pair of ribbon type optical fibers each composed of four optical fibers, particularly illustrating that their joint end surfaces are ground at a right angle relative to the longitudinal direction of the optical connector, and FIG. 8(b) is a sectional side view of the optical connector taken along line A--A in FIG. 8(a).
Joint end surfaces 56a and 56b of a pair of ferrules 55a and 55b each having a rectangular cross-sectional contour and including four naked optical fibers 52a and 52b with sheathes 51a and 51b peeled therefrom are ground at a right angle relative to the longitudinal direction of the optical connector.
The joint end surfaces 56a and 56b are jointed to each other by inserting the ferrules 55a and 55b into an alignment sleeve 57.
With respect to the conventional optical connector constructed in the above-described manner, since there inevitably arises a minor machining error during a grinding operation performed for the end surfaces of the optical fibers, they do not come in close contact with each other when they are jointed to each other in the alignment sleeve 57. This leads to the result that there arises a joint loss of about 0.35 dB derived from a Fresnel loss due to the presence of an air layer between the adjacent optical fibers. In addition, when an incident light beam L is reflected at the joint surface and returns to a light source (not shown), a reflective return loss is caused, resulting in an undesirable loss of about 10 db.
In a case of ferrules for an optical connector having single cored-optical fibers used therefor, to obviate the foregoing drawback, another proposal has been made as to a method of eliminating Fresnel loss and reducing reflective return loss by bringing a pair of single cored-optical fibers into direct contact with each other at apexes of spherical surfaces of the optical fibers. Additionally, as a modified embodiment, it is thinkable that reflective return loss could be reduced to an ultimate extent by grinding the end surfaces of the ferrules with an inclination angle of eight degrees or more relative to a plane perpendicular to an axis of the optical fibers so as to assure that a reflected return light beam is irradiated only to a clad layer of each optical fiber without any return to the light source.
However, since ferrules for ribbon type optical fibers are used in a different application field from that of ferrules for single cored-optical fibers, a variety of research is presently being conducted for the development of ribbon type optical fibers, particularly with respect to the contour of the end surface of each optical fiber as well as a method of grinding the end surface of the same. However, many problems are still unsolved.